1. Field of the invention
The present invention relates to an optical head, and particularly, to an optical head used for high-density optical recording and reading onto and from optical recording media.
2. Description of the Related Art
In recent years, in the field of optical memories for optical recording and reading of information, an optical head being capable of recording a larger amount of information, that is, having a remarkably improved recording density has been required with increase in speed of computers and development of multimedia. As a technology to record and read information at high densities, a near-field light recording technology has been proposed. In conventional optical memories using laser beams, the upper limit of the recording density depends on the diffraction limit of light, so that only a mark of approximately the wavelength of light (approximately several hundred nanometers) can be recorded and read out.
In an optical memory using a near-field light phenomenon which has been proposed in recent years, a mark of several tens of nanometers smaller than the diffraction limit of light can be written as a signal and read out by applying light for recording and reading under a condition where a probe having a fine opening of not more than the wavelength of light or an optical head using a solid immersion lens has been brought near to the recording medium (optical disk) until it is only several tens of nanometers away therefrom.
In a case where information on a recording medium is read out by use of near-field light, reflected light converted into propagation light and reflected is detected. However, since the use efficiency of near-field light is, intrinsically, considerably low, it is necessary to efficiently detect the reflected light.
As a technology to detect the reflected light for reading, a near-field optical microscope in which a fine opening array and a photoelectric array are integrally formed is disclosed in Japanese Laid-open Patent Application No. 5-164968. Moreover, an integrated probe in which a photodetector is integrated is described on page 579 of Applied Physics Letter No. 68 (1996). However, it is the present state that desired detection efficiency cannot always be obtained even with these detection technologies.